An ongoing project on maternal-fetal transmission of simian AIDS resulted in a number of rhesus monkey infants being delivered by Caesarean section and another number of infants being removed from their dams within moments of birth. The c-section infants were introduced within a few hours of "birth" to the females which had had their newborn infant removed, and these females were returned to their previous social group with the new, but unrelated, infant. This situation provided an opportunity to compare the behavior and activity of foster infants with normal infants to determine if adult rhesus monkeys automatically "know" their own genetic offspring. Four foster infants from one social group were matched for age and sex and mother's parity with four normal infants from a different social group, and focal animal observations were carried out from July-December of 1995. Infant activity (still, move, feed, explore, play), mother activity (still, move, feed), mother-infant interactions, and infant interactions with members of other age-sex group were noted. There were no differences in infant or mother activity, and there were no differences in mothers' or other group members' interactions directed toward the foster and normal infants. Since there were no differences in the way group members or mothers treated the foster infants (no genetic relatedness) vs. the normal infants, the hypothesis that it is familiarity rather than innate kin recognition that organizes rhesus monkey social lives is supported.